1. Field of the Invention
The present invention relates to a honeycomb structure and a manufacturing method thereof. More particularly, it relates to a honeycomb structure onto which a large amount of catalyst can be carried while suppressing an increase in pressure drop and which can suitably be used as a catalyst carrier, and a honeycomb structure manufacturing method by which such a honeycomb structure can be manufactured.
2. Description of the Related Art
Heretofore, there have been suggested exhaust gas purification devices where a catalyst for purification is carried onto a catalyst carrier, to purify components under purification included in exhaust gases discharged from engines for a car and for a construction machine, an industrial stationary engine, a combustion apparatus, and the like. Examples of the components under purification include carbon monoxides (CO), hydrocarbons (HC), nitrogen oxides (NOx), and sulfur oxides (SOx). As a catalyst carrier for such an exhaust gas purification device, there is used, for example, a honeycomb structure including porous partition walls by which a plurality of cells that become through channels of a fluid are partitioned (e.g., Patent Documents 1 and 2). The catalyst for purification is carried onto the surfaces of the partition walls of the honeycomb structure and the insides of pores of the porous partition walls.
The honeycomb structure can be manufactured by, for example, the following manufacturing method. First, forming raw materials containing a ceramic raw material are mixed and kneaded to obtain a kneaded clay. The obtained kneaded clay is extruded and formed into a honeycomb shape to obtain a honeycomb formed article. The obtained honeycomb formed article is dried and fired, whereby the honeycomb structure can be manufactured. Moreover, as a manufacturing method of a porous ceramic having a high porosity and a large strength, the following manufacturing method and the like have been disclosed. The manufacturing method includes a step of forming a mixture containing water absorptive polymer particles having an amount of water to be absorbed at a pressure of 980 Pa in a range of 5 to 30 ml/g, the ceramic raw material and water, and a step of heating and firing the obtained formed article (e.g., Patent Document 3).    [Patent Document 1] JP-A-2009-242133    [Patent Document 2] Japanese Patent No. 4246475    [Patent Document 3] Japanese Patent No. 4540094
In honeycomb structures disclosed in Patent Documents 1 and 2, however, when an amount of a catalyst to be carried becomes large, a large amount of catalyst is deposited on the surfaces of partition walls. In consequence, there have been problems that sectional areas of cells which become through channels of a fluid decrease and that a pressure drop increases.
Moreover, in a manufacturing method disclosed in Patent Document 3, it has been suggested that as water absorptive polymer particles contained in a forming mixture, particles having an average particle diameter in a range of 1/30 to 1/1 on the basis of a thickness of a ceramic formed article are used. However, even when such water absorptive polymer particles are used, the amount of the catalyst to be carried onto the obtained honeycomb structure is limited. In consequence, there has been demanded the development of a honeycomb structure onto which a larger amount of the catalyst can be carried and in which an increase in pressure drop does not easily occur.